EP2008216A2

EP2008216A2 - Apparatus and methods for constructing and packaging waveguide to planar transmission line transitions for millimeter wave applications

Info

Publication number: EP2008216A2
Application number: EP07870421A
Authority: EP
Inventors: Brian P. Gaucher; Janusz Gryzb; Duixian Liu; Ullrich R. Pfeiffer; Thomas M. Zwick
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 2006-03-31
Filing date: 2007-01-23
Publication date: 2008-12-31
Also published as: JP2009531923A; JP5147826B2; TWI414103B; CN101496279B; US20070229182A1; CN101496279A; TW200807798A; US7479842B2; EP2008216A4; WO2008062311A3; WO2008062311A2

Abstract

Waveguide-to-transmission line transitions are provided for broadband, high performance coupling of power at microwave and millimeter wave frequencies. In one aspect, a transition apparatus (10) includes a transition housing (11) comprising a rectangular waveguide channel (C) and an aperture (13) formed through a broad wall (11a) of the rectangular waveguide channel (C), a substrate ( 12) having a first surface and a second surface opposite the first surface, mid a planar transmission line (12a) and a planar probe (12b) formed on the first surface, wherein the planar transmission line (12a) comprises a first conductive strip and a second conductive strip, wherein the planar probe (12b) is connected to, and extends from, an end of the first conductive strip, and wherein an end of the second conductive strip is terminated by a stub and wherein the substrate (22) is positioned in the aperture (13) such that the printed probe (12b) protrudes into the rectangular waveguide channel (C) at an offset from a center of the broad wall (11a) and wherein the ends of the first and second conductive strip are aligned to an inner surface of the broad wail (11a) of the rectangular waveguide channel (C).

Description

APPAR \Tl 'b AND MklΗODS FOR CONSTRl C I I\G WO P \CK\G1NC

WΛVEGIWDE TO PLANAR TRANSMISSION LINE TRANSITIONS FOR MILLIMETER WA* E APPLICATIONS

1 ethnical Field of the ImeπfuHi s 1 he piessem im entson relates Io apparatus and methods lor constructing wax eguide- to-Uansmission line transitions that pioude broadband high performance coupling of powei at rasαowa\ e and milhmetei Λ\ a\ e frequencies The present im eotton fuithet relates to apparatus and methods for constructing compact w ireless communication modules in which mιero\\a\ e sntegiated circuit chips and oj modules ate uutjgiaih packaged with s π \\a\ eguide-to-uansm!ssion line lransrlion structures pio\ idmg a raodutai component that can be mounted to a s»tandaid \\ax eguide flange

Background

Iii general microv\a\ ύ and miJhmeicr-v\a\ e (MVIW) communication s\ stems are const! ucled with v arious components and subcomponents such as ieceu eu transmitter and

1 ^ {ranscen er modules as w ell as other passn e and actn e components, which ase fabricated u\mg MK (M!cio\\a\e Initiated Cucusti and oi VINOC (Monohthic Microwav e Integrated C lrcuit) technologies lhe s\ stem coniponents-'suhcomponents can be uitci connected usmi. \ aiious t\ pes of iransmissjion media such a.s punted tιansmij>siυn lines (e g , miciostiip slυiiine CPW (cυplanai ws\ eguide). t PS (copianai stπphne) \C PC

2u (as> mmetric coplanar stupline) etc ) oi coaxial cables and xsax eguides

Punted U ans mission hnes ase wideh used rn micros a\ e and VJMW cncinh Io pso\ ide packagc-!e\ cl or circuit boaid-lex ei mteicoiiiiecb between semiconductor chips {KT inteyratad cucusts) and between semiconducloi chips and tiamnnttej ox recen ei atitemiai Moreov er, printed trati&misston hne& me well minted for signal piopagation on the

^ surface of d scmicondiictoi integiated circuit For instance CPW tiansmission hnes die wideK used m MMiC designs due to {heir umpianai nature, low dispeision and high compatibility vith actn e and passive dex ices How ev er, printed tiansmissjoii hnes max be subject to paiaMtic modes and me teased losses at high frequencies On the other hand metallic wax cguides (e g i ectangular circular, etc ) are suitable for signal transmission

^o o\ er lai s>er distances and at high pow er ia\ els in a lovx -loss mannei Furtheπnoie, wax (jguidei ma\ be shaped into a highh dnectix c antennas or ma\ be used for device characteii/ation When constructing microwave. RF or MMW systems, it may necessary to couple a printed transmission line with a waveguide using a coupling structure referred Io a "transition^"'. Transitions are essential for integrating various components and subcomponents into a complete system. The most common transmission line-to-waveguide 5 transitions are microsmp-to-waveguide transitions, which have been widely studied. While considerable research and development has been dedicated to such transitions, comparatively less effort has been applied to establish suitable transitions from CPW. CPS or ACPS transmission lines to rectangular waveguides. CPW and CPS transmission lines are particularly suitable (over microstrip) for high integration density MlC and MMlC

10 designs. In this regard, it is highly desirable to develop broadband, low-loss and well matched transitions between waveguides and CPW or CPS printed transmission lines or monolithic microwave integrated circuits (MMlCs) which can be used to design high performance systems.

Summary of the Invention

!5 Exemplary embodiments of the invention generally includes apparatus and methods for constructing waveguide-to-transmission line transitions that provide broadband, high performance coupling of power at microwave and millimeter wave frequencies. More specifically, exemplary embodiments of the invention include wideband, low-loss and compact CPW-to-rectangular waveguide transition structures and ACPS (or CPS)-Io-

20 rectangular waveguide transition structures that are particularly suitable for microwave and millimeter wave applications.

More specifically, in one exemplars' embodiment of the invention, a transition apparatus includes a transition housing and transition carrier substrate. The transition housing has a rectangular waveguide channel and an aperture formed through a broad wall

25 of the rectangular waveguide channel The substrate has a planar transmission line and a planar probe formed on a first surface of me substrate. The planar transmission line includes a first conductive strip and a second conductive strip, wherein the planar probe is connected to, and extends from, an end of the first conductive strip, and wherein an end of the second conductive strip is terminated by a stub. The substrate is positioned in the

30 aperture of the transition housing such that the printed probe protrudes into the rectangular waveguide channel at an offset from a center of the broad waJl and wherein the ends of the first and second conductive strip are aligned to an imier surface of the broad wall of the rectangular waveguide channel.

The printed transmission line may be a CPS (copianar sfripline). an ACPS (asymmetric copianar stripiine) or a CPW (copianar waveguide). One end of the rectangular 5 waveguide channel is close-ended and provides a back short for the probe. In one exemplary embodiment the backshort is adjustable. Another end of the rectangular waveguide channel is opened on a mating surface of the transition housing. The mating surface can interface with a rectangular waveguide flange The transition housing may be formed from a block of metallic material. Alternatively, the transition housing can he io formed from a plastic material having surfaces that are coated with a metallic material.

In another exemplary embodiment of the invention, the aperture of the transition housing is designed with a stepped-width opening to enable alignment and positioning of the substrate in the aperture and the rectangular waveguide channel.

In yet another exemplarv embodiment of the invention, the stub at the end of the

! 5 second conductive strip is connected to edge wrap metallization for parasitic mode suppression. The edge wrap metallization may be electrically connected to a metallic surface of the transition housing. The edge wrap metallization may be connected to a ground plane on a second surface of the substrate. The edge wrap metallization may be galvanically isolated from the transition housing.

20 hi yet another embodiment of the invention, the transition housing includes a tuning cav ity formed on a second broad wall of the rectangular waveguide channel opposite and aligned to the aperture. The tuning cavity can be shorted by an adjustable backshort element to provide a mechanism for impedance matching.

Exemplar}' embodiments of the invention further includes apparatus and methods for

25 constructing compact wireless communication modules in which microwave integrated circuit chips and/or modules are integrally packaged with waveguide-to~iransmission line transition structures providing a modular component that can be mounted to a standard waveguide flange.

These and other exemplarv embodiments, aspects, features and advantages of the

3i) present invention will be described or become apparent from the following detailed description of exemplary embodiments, which is to be read in connection with the accompanying drawings. Brief Ilescription of the Prayings

FlGs I A and 1 B aie schematic perspectiv e uevv^ oi a transmission. Sine to waΛ eguide tiansmon appaiatus (10) accoiding to an exemplar} embodiment of the inv ention

> MG 1C JS a schematic illustration of the rectangular w av eguide ca\ il\ C illustrating a dominant TT 10 piopagation mode

FIG 2 ss a schematic pesspectπ e \ iev\ oJ a package as^erabh (20) including a ttansmission itne-to-vun egmde transition module that is inlegralh packaged vulh external cucuitn accoiding to an exemplar} embodiment of the in\ ention i π FIGS 3Λ- ID illustrate structuial details of a metallic ttansition housing (30) accoiding io an exemplaiΛ cnibodiniem of the ιn\ ention

MGS 44 -4C are schematic peuφectn e \ ιe\\s of a tiansmiswon hoc to wax eguidc transition apparatus according to an exemplan «πibodimenl of the m\ ention

FIGS 5Λ - 5C ate schematic perφectn e \ lews of a tπuisraj^sion line to ua\ eguide ! "< ttansjlion apparatus accordnig to an evenψlan embodiment of the im enfion

HCj o schematicaJh illustiatess a conductoi -backed C PW feed stiuctuie in w hich hal t-ua edge w i apping metallization is used for suppressing undesired v ax eguidc modes and icsonancos. accoidmi. to an e\emplan embodiment of the im ention

MG 7 Kchemaucalh illυstiatcs a non conductor-backed CPU feed structure Jn 2» which haU-\ ui *is>e v\ rappmg tnetalh/alion is used for suppressing undesired \sa\ egusde modes and iesonances according to an e\emρlan embodiment of the m\ ention

MG 8 schematicalh iUustialci a conductor-backed CPS feed structure in which haJf-λ ia edge w rapping metallization i_, used for suppiesssing mule^red w aΛ βguide modes and resonances, accoiding to an exemplan. embodiment of the inv ention

:s FIG 9 schematicalh illustrates a non-conductor-backed CPS feed sUuctuie m w hich hal f-x ia edge \s rapping metalh/atjon is used for suppressing undesired v\ av eguide modes and je^onances according to an exemplan embodiment of the inv enlion Detailed Description of £\emplar> Embodiments MGs 1 \ and I B aie schema lie perspectπ e x iev s of a transmission line Io "^O \\a\ egυide transition apparatus ( 10) according to ai exemplan embodiment of the j m en Ii on More ^pecificalh FiGs I A and 1 B schematicall^y depict a tiansition apparatus ( 10) for coupl mg electiomagnetic Signals betw een a iectangular \\ a\ eguide (e g \Λ R I5) and a printed transmission line using an E-plane probe-type transition, according to an exemplary embodiment of tiie invention. The transition apparatus (10) comprises a metallic transition housing (I i) (or waveguide block) which has an inner rectangular waveguide cavity C (or rectangular waveguide channel) of width α (broad wall) and height h (short 5 wall). An aperture (13) is formed in a Front wail (1 Ia) of the waveguide block (1 1 ) through a broad vvaJl of the rectangular waveguide cavity C to provide a transition port Pr for insertion and support of a planar transition substrate (12) having a prmted transmission line (12a) and printed E-plane probe Cl 2b). The transition substrate (12) is positioned in the aperture (13) such that the probe (12b) protrudes into the waveguide cavity C through the so broad wall of waveguide cavity C. One end of the waveguide cavity C is opened on a side wall (11 b) of the transition housing ( 1 1 ) to provide a waveguide input port /V . The other end of the waveguide cavity C is short-circuited by sidewali (Uc) oFthe transition housing (1 1), whereby the inner surface of the metallic sidewali (1 Ic) serves as a backshort B for the probe (12b).

! 5 in one exemplars' embodiment of the invention, the probe C 12b) is an E-plane type probe which is designed to sample the electric field within the rectangular waveguide cavity C where the rectangular waveguide is operated in the dominant TE_iy mode. As is well- known in the art, in a rectangular waveguide, the electric field is norma! to the broad sidewali and the magnetic field line is normal to the short sidewali. By way of example,

20 FfCi-, 1C is a schematic illustration of the rectangular waveguide cavity C where the short sidewalis Cb) extend in the x -direction (coplanar with x-z plane), the broad sidewaJis (a) extend in the y-direclion (coplanar with y-z plane), and where the cavity C extends in the indirection (i.e.. tli e direction of wave propagation along the waveguide channel). FIG. 1C further illustrates an £^' field for the TE_JO mode is in the x-> plane (normal to the broad

25 walls) where the maximum positiv e and negative voitage peaks of the TE wave travel down the center of the waveguide broad walls (a) and the voltage decreases to zero along the waveguide short walls (h).

In this regard, in the exemplary embodiment of^'FΪGs. IA and IB. the substrate (12) with the printed probe (12b) is inserted through the transition port /V in the broad sidewali

30 { 1 1 a) such that the probe ( 12b) is positioned transverse (normal) to the direction of wave propagation (i.e., ^-direction in FIO. 1 C) and such that the plane of substrate (12) is positioned tangential to the direction of wave propagation (i.e.. plane of substrate ( 12) is copianar with x-z plane in FlG. 1 C). The sidewali (Hc) of the metal block (J l ) serves as a backshort B such thai the inner surface of the side wall (1 Ic) is placed in a certain distance (close to a quarter-wavelength for TE so mode) behind the probe ( i 2b) to achieve good transmi ssi on properti es, 5 It is to be understood that FJGs, IA and 1 B schematically depict a general framework for a waveguide-lo-planar transmission line transition apparatus according to an embodiment of the invention. The printed E-pIane probe (12b) may have any suitable shape and configuration which is designed to sample the electric field within the rectangular waveguide cavity C. The printed transmission line (12a) may be any suitable feed structure io such as a printed CPW (copJanar wave guide) feed. ACPS (asymmetric copianar stripline) feed, or CPS (copianar stripline) feed. For example, as described in further detail below. FlCtS, 4A-4C, 5A-5C and 6-9 illustrate transition structures according to various exemplary embodiments of the invention, which may be constructed with transition substrates having printed conductor-backed aid non-conductor backed CFW and CPS feed

! 5 fines and planar probe transitions, as will be explained in further detail below.

In other exemplary embodiments of the invention, the exemplary transition structure of FlGs, I A-IB can be integrally packaged with electronic components, such as MlC or MMIC modules to construct compact package structures. For instance. FΪG. 2 is a schematic perspective view of a package assembly (20) including a transmission line-to-

20 waveguide transition module that is integrally packaged with external circuitry according to an exemplary embodiment of the invention, The exemplars¹ package (20) includes a transition housing (2i) (or waveguide block) having an inner rectangular waveguide channel C. The transition housing (21) has a front wail (21 a) with an aperture extending through a broad wall of the inner rectangular waveguide channel C providing a transition

25 port Pr A transition substrate (22) with a printed transmission hne and E-plane probe is inserted into the waveguide cavity through the transition port Pr

One end of the rectangular waveguide channel C is opened on a sidewall (21c) of the transition housing (2 i) to provide a backshort opening Ba, and the other end of the rectangular waveguide channel is opened on a sidewali (2 i b) of the transition housing (21 )

30 to provide a waveguide input port P».-, The backshort opening B₀ on the sidewall (21c) of the waveguide housing (2.1 ) is formed to allow insertion of a separately fabricated backshort element to short-circuit the end of the waveguide cavity C exposed on the side wal! (2IcK and provide an adjustable E-pJane hackshort for purposes of impedance matching and {tming the transition.

The transition substrate (22) is supported by a bottom inner surface of the transition port/'? opening and a support block (23) which extends from the front wail (21a) of the 5 transition housing (2 i ) and lias a top surface that is coplanar with the bottom inner surface of the transition port Pr opening. The transition housing (21 ) and support block (23) are disposed on a base structure (24). Ia one exemplary embodiment, the transition housing (21). support block (23) and base plate (24) structures form an integral package housing structure that can be constructed by machining and shaping a metallic block, or such io components may be separate components that are bonded or otherwise connected together.

A printed circuit board (26) having a MMlC chip (27) and other RF integrated circuit chips, for example, is mounted on the base (24) such that the surface of the chip (27) is substantially coplanar with the surface of the transition substrate (22). One or more bond wires (28) provide I/O connections between the transmission line feed on the transition

! 5 substrate (22) and I/O contacts on the chip (27). in the exemplary package design, the plane of substrate (22) is positioned tangential to the direction of wave propagation, which allows the externa! electronic components to be located in the same plane of the substrate (22), thus, simplifying placement and integration of the components

The package structure (20) schematically illustrates a method for integrally

20 packaging a MMW or microwave chip module with a rectangular waveguide launch according to an exemplary embodiment of the invention. The exemplar}' package (20) provides a compact, modular design in which a MMiC transceiver, receiver, or transceiver module, for instance, can be integrally packaged with a rectangular waveguide launch. The package (20) is preferably designed to be readily coupled to a standard flange of a

25 rectangular waveguide de\ ice (25) such that the waveguide port on surface (21 fa) is aligned to and interlaces with the waveguide cavity of the rectangular waveguide device (25). For instance, the package (20) can readily interface to a standard VVRl 5 waveguide flange.

It is to be understood that the exemplary embodiments of FIGs. I A-- IC and 2 are high-lev el schematic illustrations of methods for constructing and packaging wav eguide

3i) transitions for various applications and operating frequencies. For instance, transition structures, which are based on the above-described general frameworks, will be discussed in further detail with reference to FIGs. 3A-3D. 4A--4C 5 A-5C and 6-9. for MMW applications (e.g., wideband operation over 50-70 GJIz for WR 15 rectangular waveguide). Waveguide transitions according to exemplary embodiments of the invention have a common architecture based on a waveguide block with an inner waveguide channel and a substrate based feed structure with the printed probe inserted into an opening in a broad 5 wall of the waveguide channel. As will be explained below, various techniques according to exemplary embodiments of the invention are employed to design wav eguide transitions providing low loss and wide bandwidth operation in a manner that is robust and relatively insensitive to manufacturing tolerances and operating environment while allowing ease of assembly.

10 In one exemplary embodiment, transition structures are designed with off-centered positioning of the transition substrate (with the printed feed and probe) along {he broad wall of the rectangular waveguide channel. With conventional, E~piane probe designs, transitions are constructed having a symmetrical arrangement where the probe insertion point is the center of the broad side wall of the waveguide. However, this conventional

! 5 technique usually does not lead to the optimal position, thus, resulting in a high input reactance limiting the bandwidth, especially for an E-plane probe loaded by a thick high dielectric permittivity substrate.

It has been investigated that an offset launch can achieve a lower input reactance over a wide frequency band, thereby allowing a broader match. The low input reactance of

20 the offset launch can be attributed to the significant reduction of the amplitudes for high order evanescent modes, being a result of the filter perturbation in the uniform rectangular waveguide by a dielectric loaded probe. Advantageously, an offset launch can eliminate the need for additional matching structures, which allows more compact solutions. Indeed, exemplar}' transition structures according to the invention do not require additional

25 matching components that extend out of the waveguide walls. Indeed, in exemplary embodiments described below, probe transitions can be directly feed by uniform CPW or ACPS/CPS transmission lines while achieving desired performed ov er, e.g., the entire WR iS frequency band.

In other exemplary embodiments of the invention, transition substrates with printed

3i) feed lines and probe transitions are designed with features that suppress undesirable higher- order modes of propagation and associated resonance effects that can lead to multiple resonance like elTects at MMW frequencies by v irtue of a conductor backed environment provided by the metallic waveguide wails. In particular, exemplary transition are designed fo suppress undesired CSL (coupled slotiine). microstrip-like and parallel wa\ -eguide modes, which could be generated due to electrically wide transition substrate with a printed feed line being disposed in a wide opening (transition port P_T K where the entire, or a 5 substantial portion of, the transition substrate with the printed feed line is enclosed/surrounded by metallic sidevvali surfaces in the transition port Pr opening. As described in detail below, edge- wrap metallization and casteilauons in the form of half-vias or half-slots may be used to locally wrap upper and lower conductors (ε g, ground conductors) on opposite substrate surfaces of CPW or CPS/ ACPS feed lines, winch are

10 disposed within the waveguide walls. Such solutions allow for effective connection of top and bottom conductors located on opposite surfaces of the transition substrate, independently of the substrate dicing tolerances and other manufacturing tolerances (e.g.. Unite radius of comers within the transition port opening), window.

^"Transition structures that are based on the above-described general frameworks, will

! 5 now be discussed in further detail with reference to FfGs 3A-3D, 4A-4C, 5A--5C and 6-9. for MMW applications. In general. FfGs, 3A- 3D illustrate an exemplar)' embodiment of a transition housing (or waveguide block) for use with a CPW-based feed structure and E- plane probe transition (FKJ. 4A- 4C) or stripline-based feed structure and E-piane probe transition (FTG. 5A-5C). Moreover. FlGs. 6-9 illustrate various embodiments for

20 constructing conductor backed and nan conductor backed CPW and CPS feed lines using half-via edge wrapping metallization for suppressing undesired modes and resonances.

More specifically. FIGS. 3A-3D illustrate structural details of a metallic transition housing (30) according to an exemplar)' embodiment of the invention. FlG. 3 A illustrates a front view of the exemplar)- transition housing (30) which generally comprises a waveguide

25 housing (31 ) and a substrate support block (32). FfCi. 3B is a cross sectional view of the transition housing (30) along line 3B-3B in FΪG. 3A and FIG. 3C is a cross-sectional view of the transition housing (30) along Sine 3C-3C in FKJ. 3A. FKJ. 3D is a back view of the transition housing (30) (opposite the front view of FlG. 3A). The transition housing (30) can be formed of bulk copper, aluminum or brass, or any other appropriate metal or alloy.

3i) which can be silver plated or gold plated to enhance conductivity or increase resistance to corrosion. The transition housing (30) can be constructed using known split-block machtning techniques and/or using the wire or thick EDM (electronic discharge machining) techniques for dimensional precision required at millimeter wave frequencies. In other exemplary embodiments, the transition housing can be formed of a plastic material using precise injection mold technique for cost reduction purposes. With plastic housings, the relevant surfaces (e.g.. broad and short wall surfaces of the rectangular waveguide channel) 5 can be coated with a metallic materia! using known techniques.

As generally depicted in FlGs. 3A--3D, the waveguide block (35 ) includes an inner rectangular waveguide channel (shown in phantom by dotted hnes m 3 A and 3D) having width - a and height ^~ h defined by inner surfaces of the front/back broad walls (31 a)/{31 b). aid the botiom/top short wails (31 e)/(31 ά) of the wav eguide block (31 ). The s 0 front and back broad walls (31 a) and (31 b) are depicted as having a thickness. /. The waveguide channel is open-ended on one side wall of the waveguide block (31 ) Io provide a waveguide port /y. The other end of the waveguide channel is closed (short-circuited) by a back.sho.rf Bl component. In one exemplars' embodiment of the invention, the hackshort FJl is a separately machined component that is designed to be inserted into the end of the

! 5 waveguide channel allowing adjustment of the backshort distance hi between lhe probe transition and the inner surface of the backshort Bl (as depicted in Fig. 3B) for tuning and matching the waveguide and transition. In such case, the inner rectangular waveguide channel would be formed with open ends on eacli side wall of the waveguide block (3.1 ). An aperture (33) is formed through the front broad wall (31a) of the waveguide

20 block (3 i ) to provide a transition port P_T for inserting a dielectric substrate with a printed transmission line and probe transition. The aperture (33) is formed having a height h and having a step-in-width feature including an inner opening (33b) of width W₁ and an outer wall opening (33a) of width W^. The bottom of the aperture (33) is formed at a height ø ' from the inner surface of the bottom short wall (31 c). The bottom inner surface of the

25 aperture ( 33) is copianar with the upper surface of the substrate support block (32 ) which extends at a distance A^* (see PIO. 3C) from the front surface of the waveguide block (31). The aperture (33) and support block provide a copianar mounting surface of length t*x for supporting a planar transition substrate. The step-in -width structure of the aperture (33) provides a mechanism for accurate, self-alignment and position of a transition substrate

30 with printed feed and transition within the waveguide aperture and cavity without using a split-block technique (no visual inspection needed). As explained below, the transition substrates are formed with a matching step-in-width shape structure enabling alignment

IO and positioning in the aperture (33) if a split-block technique is applied for positioning the transition substrate with the probe within the waveguide aperture, the aperture (33) can be formed with a uniform narrow opening, e.g.. having width Wt of the inner opening (33b).

A timing cavity ( 34) (or tuning stub) is formed on the broad wall (31 b) of the 5 waveguide channel opposite the transition port aperture (33). As depicted in FlG. 3D, the tuning cavity (34) is essentially an opening formed in the broad wall (31b) in the waveguide channel, which is aligned to the inner opening (33b) of the aperture (33) and having the same dimensions h x W₁. In addition, the tuning cavity (34) is short-circuited using a separately machined backsliort element B2 that can be adjustably positioned at a distance hi s 0 from the opening of the tuning cavity (34) (i.e. , from the inner surface of the broad wall (3.Ib)). The tuning cavity (34) with adjustable backshort B2 provides an additional tuning mechanism for matching the characteristic impedance of the waveguide port and the characteristic impedance of fhe printed feedline and probe transition.

In one exemplary embodiment, the tuning cav ity (34) and inner opening (33b) of the

! 5 aperture (33) can be created together in a single manufacturing step using wire EDM machining to machine through the entire width of the metal block that is milled to form the transition housing (30). The narrower opening (33b) (width Wi) can be machined using an EDM technique for precision, while the wider opening (33a) (width W^) can be formed using classical techniques with less precision smee the dimensional accuracy for WK? has

20 minor influence on fhe transition performance A thick EDM process may be used to form the opening (33) when the tuning cavity (34) is not desired.

In exemplary transition designs, when forming the transition port /V in the broad wall, there are inherent limitations for machining techniques (even as precise as EDM) which can not provide square openings - the machining results in openings with finite

25 radius comers (denoted as '^'R{^~ and "⁴Rj" in FIG. 3A). For instance, wire EDM techniques yield openings with a comer radius of 4-5 mils, wherein thick EDM techniques can yield opening with a smaller comer radius of 2 .mils. Because of these inherent limitations, the aperture (33) openings are formed with rounded comers. As such, a transition substrate would have to be made smaller than the aperture width {W_lf W₁), or the transition substrate

30 would not seat properly and contact the inner side wall surfaces.

FIGS, 4A-4C are schematic perspective views of a transmission line to waveguide transition apparatus according to an exemplar}' embodiment of the invention, hi particular,

I l FlGs 4A-4C illustrate an exemplary CPW-to-rectangυlar waveguide transition apparatus (40) that is constructed using the exemplary metallic transition housing (30) (as described with reference to FlGs. 3 A -3D) and a planar transition substrate (41) comprising a primed CPW transmission line (42) and E- plane probe (43). FIG. 4A illustrates a front view of the 5 exemplars' transition apparatus (40) with the transition substrate (41) positioned in the aperture (33) (transition port /Y). FlG. 4B is a cross sectional cut vievv of the transition apparatus (40) along line 4B-4B in FIG. 4A and FIG. 4C is a cross-sectional cut view of the transition apparatus (40) along line 4C-4C in FlG. 4A.

The transition substrate (41) comprises planar substrate hav ing a stepped width s 0 structure comprising a first portion (4 i a) of width Ws and a second portion (41 b) of reduced width Ws \ which provides self-aligned positioning of tlie substrate (41) with {he stepped width aperture (33). in the exemplars- embodiment, the width Ws of the substrate portion (41a) is slightly less than the width W; of the outer portion (33a) of the aperture (33) and the width Ws' of the substrate portion (41 b) is slightly less than the width W_} of the inner

15 portion (33b) of the aperture (33), which takes into account the rounding comers of the inner and outer openings (33a) and (33b) as explained above.

The substrate (41) comprises top surface metallization that is etched to form the CPW transmission line (42) on the substrate portion (4Ia) and planar transition with the E- plane probe (43) on the substrate portion (41b), Hie substrate portion (41 b) further includes

20 a transition region (44) where the CPW transmission line (42) is coupled to the probe (43). In the exemplary embodiment, the transition region (44) can be considered the region located between the walls of the inner opening (33b) of the aperture (33) and bounded by the inner surface (31 a) of the broad wall of the svav eguide block (31 ) and the interface between the inner and outer openings (33b) and (33a).

25 The CPW transmission line (42) includes three parallel conductors including a center conductor (42a) of width n^>, which is disposed between two ground conductors (42b) of width g. and spaced apart from the ground conductors (42b) at distance s. The probe (43) is depicted as a rectangular strip of width Wp and length Lp. which is connected to. and extends from the end of the center conductor (42a) of the CPVV (42). The end of the

30 substrate portion (41 b) extends at a distance Ls from the inner surface (31a) of the waveguide broad wall (31 ). where Ls is greater than Lp. The ground conductors (42b) of the CPW (42) are terminated by stubs (44a) of width gs in the transition region (44). where

12 stubs essentially form a 90 degree band from the end of the ground conductors (42b) toward {he sidewalis of the substrate adjacent the metallic wails of the inner opening (33b) of the aperture (33).

FIGS. 5A-5C are schematic perspective views of a transmission line to waveguide 5 transition apparatus according to another exemplary embodiment of the invention. In particular. FIGs. 5A-5C illustrate an exemplary ACPS-to-rectanguiax waveguide transition apparatus (50) thai is constructed using the exemplary metallic transition housing (30) (as described with reference to FlGs. 3A-3D) and a planar transition substrate (51 ) comprising a printed ACPS transmission line (52) and E-plane probe (S3). FIG, 5A illustrates a front io view of the exemplars¹ transition apparatus (50) wi Ih the transition substrate (51 ) posi boned in the aperture (33) (transition port /V ). FlG. 5B is a cross sectional cut view of the transition apparatus (50) along line 5B-5B in FJG. 5A and FJG. 5C is a cross-sectional cut view of the transition apparatus (50) along Sine 5C-5C in FlG, 5 A.

The transition substrate (5 J ) comprises planar substrate having a stepped width

! 5 structure comprising a first portion (51 a) of width Ws and a second portion (5 Ib) of reduced width Ws. \ which provides self-aligned positioning of the substrate (51) with the stepped width aperture (H). Jn the exemplary embodiment, the width Ws of the substrate portion (51a) is slightly less than the width W ₂ of the outer portion (33a) of the aperture (33) and the width Ws* of the substrate portion (51b) is slightly less than the width W₁ of the inner

20 portion (33b) of the aperture (33). which takes into account the rounding comers of the inner and outer openings (33a) and (33b) as discussed above.

The substrate (5 J ) comprises top surface metallization that is etched to form the CPS transmission line (52) on the substrate portion (51 a) and planar transition with the E-plane probe (53) on the substrate portion (51 b). The substrate portion (51b) further includes a

25 transition region (54) where the CPS transmission line (52) is coupled to the probe (53). In the exemplan- embodiment, the transition region (54) can be considered the region located between the walls of the inner opening (33b) of the aperture (33) and bounded by the inner surface (31 a) of the broad wall of the waveguide block (31 ) and the interface between the inner and outer openings (33b) and (33a).

30 The CPS transmission line (52) includes two parallel conductors including a first conductor (52a) of width w, and a second conductor (52b) of width g. and spaced apart at distance s. When the widths of the conductors (52a) and (52b) are the same {w^:::g), the transmission line (52) is referred to as a CPS .line, which can support a differential signal where neither conductor (52a) or (52b) is at ground potential. When the widths of the conductors (52a) and (52b) are different (e.g.. n> < g), the transmission line (52) is referred to as an asymmetric CPS (ACPS) line. In the exemplary embodiment an ACPS feed line is 5 shown, where conductor (52b) is a ground conductor. The probe (53) is depicted as a rectangular strip of width Wp and length Lp. which is connected to. and extends from the end of the first conductor (52a) of the feed line (52). The substrate portion (5 I b) extends at a distance Ls from the inner surface (31 a) of the waveguide broad waif (31 ), where Ls is greater than Lp. The ground conductor (52b) is terminated by a stub (54a) of width #s in the s o transition region (44), where the stub essentially forms a ¹X⁾ degree bend from the end of the conductor (52b) to the substrate side wall adjacent to the metallic wail of the inner opening (33b) of the aperture (33).

The exemplars' transition carrier substrates (4! ) and (51 ) can be constructed with conductor-backed feed line structures with no galvanic isolation from the metallic

! 5 waveguide walls, or constructed with non-conductor backed feed line structures with galvanic isolation from the metallic waveguide waifs. For instance, FlGs, 6 and S schematically illustrate exemplary embodiments of the transition carrier substrates (41) and (51) constructed having full ground planes formed on the bottoms thereof to provide conductor-backed CPW and ACPS feed Sines structures. Moreover, FiGs. 7 and 9

20 schematically illustrate exemplar)' embodiments of the transition carrier substrates (41 ) and (51) constructed with noti conductor-backed CPW and ACPS feed lines structures.

In particular, referring to FIG. 6. the transition carrier substrate (41 ) has a bottom ground plane (45) that is formed below the substrate portion (41a) and the transition region (44) providing a conductor-backed CPW structure. The portion of the substrate (41 b)

25 below the probe (43) that extends past the inner surface of the broad wall (31 a) has no ground plane. Similarly, as shown in FiG. 8. the transition substrate (51 ) has a bottom ground plane (55) that is formed below the substrate portion (51a) and the transition region (54) providing a conductor- backed CPS structure. The portion of the substrate (5 Ib) below the probe (53) that extends past the inner surface of the broad wall (31 a) has no ground

30 plane. The transition earner substrates (41 ) and (51 ) cai be fixedly mounted in the transition port using a conductive epoxy to bond the ground planes (45), (55) to the metallic waveguide surface (no galvanic isolation). It is to he understood that FIOs, 6 and 8 illustrate

14 an exemplars' embodiments in which the transition substrates (4J ) and (51 ) in FIGs. 4B and 5B, for example, are formed with a uniform width (i.e.. no stepped width as shown in FfGs, 4B and 5B).

The exemplary conductor-backed CPW (CB-CPW) and conductor-backed ACPS 5 (CB-ACSP) designs provide mechanical support and heat sinking ability as compared to conventional CPW or ACPS. Moreover, conductor-backing is a natural environment for CPW or CPS feed hnes when connecting with waveguides (through the metal walls) being the metal enclosures, However, conductor backed CPW and CPS designs are subject to excitation of parallel waveguide and microslrip-like modes at mm-wave frequencies io resulting in a poor performance due to mode conversion at discontinuities and the associated resonance-like effects that may result due to the large (electrically large) lateral dimensions of the transition structure. Furthermore, a CPW can support two dominant modes, namely the CPW mode and the CSL (coupled sloliine) mode, the latter being parasitic in this case, in this regard, methods are provided to suppress high-order modes

! 5 and resonance effects by wrapping the ground conductors and bottom ground planes of the CB-CPW or CB-CPS feed staictures printed on both sides of the substrate carrier.

For example, in the exemplary embodiments of FiGs. 4B and 5B. the local wrapping can be realized by plating techniques over the partial length Li of the substrate side wall in the transition regions (44) and (54) or by the so-called "half-a-via^"' wrapping. By way of

20 example, FlG. 6 schematically illustrates a conductor-backed CPW feed structure such as depicted in FiG. 4B, where the end portions of the ground conductors (42b) are connected to the ground plane (45) on the bottom of the substrate portion (4J a) (shown in phantom) along length L) in the transition region (44) using a half-via edge wrapping metallization (46). Similarly, FIG. 8 schematically illustrates a conductor-backed CPS feed structure

25 such as depicted in FlG, 5B₅ where the end portion of the ground conductor (52b) is connected to a ground plane (55) on the bottom of the substrate portion (51a) (shown in phantom) along length Li in the transition region (54) using ahalf-via edge wrapping metallization (56). ϊn the exemplary transition designs, the use of via-edge wrapping achieves an effective connection of top and bottom ground elements located on the

30 transition substrates, providing a mode suppression mechanism that is independent of the substrate dicing tolerances and a finite radius Rt and/or R> of the inner and outer openings (33a) and (33b) of the aperture (33),

15 As described abov e, the exemplan transition structures for conductor-backed feed lines designs raa> be constructed using edge wrap metallisation and eiectπcal connection to connect the upper and low er ground elements on opposite sides of the substrate for mode suppression purposes With non conductor-backed CPW and CPS designs such as depicted > in FJGs 7 and *>„ the transition substrates are attached to the metallic wa\ egmde w alls using a non-conductiv e adhesn e

In the ptevioush described designs with the condυctoi -backed substrates when attached using non-condυctn e epow , the metallic w av eguide walls and the solid metal on {he backside of the substrate in effect create a paialiei w av eguide structure, w hich can

1» potentialh lead to eneigv leakage and paiasitic resonance effects To ax oκi this piobϊem. non-conductor-backed OPW and ACTS <oi CPS)-lo-rectangu!ai wav eguide tiansition structures with gah anic isolation to the metal waveguide block are designed with special mode suppression techniques* in which conductive strips are formed on the bottom of the transition substrates and connected to the top ground conductors of the feed structures Λ ia

! "< edge w rapping This struct ute pteΛ cnt.s the propagation of both the paialiel W G and the othei pai"asitic modes as mentioned abov e, specific to the conductor-backed designs

For example. FIG 7 ichematicalK iliustiaics a non-conductoi -backed CP^ feed structure based on the exemplar} design shown in FlG 4B In this embodiment, the substrate carrier (4! ) w ould not be electrical!) connected to the metallic w av eguide housing

2» usmg a conducts e bonding material, but rather attached to the metallic w a\ eguide housing using some non-conducttv e epo\> hav ing well known dielectric properties for the frequency range of mleiest In FIG 7. edge v\ tapping half-Ma πietaili/ation (46) w ouid be attached to a metallic "ground^" pattern (47 ) on the bottom side of the substiate carrier (41 ) in the transition region (44) to pi event propagation of paiasitic modes as mentioned above In

;s effect, the bottom metallization patterns (47) would be suspended m et (tnsuUrted from) the metal .sutfnce of the vvav egmde housing in the apeitures bs Mttue of the non-conductive epo\v bonding the meta! patiein (47 ) to the metallic was sguide suiface The number, position, width and length of the metal fingers {47} and v ia wrapping (4^) w ould be designed as needed The designs can have more wrapping points along the length of the

TO feed hnes. depending on {he required probe length Of special importance is also the

.spacing (filled with a non-conductn e epo\> ) between the bottoms of the substiate and the opening, which is kept low for an exemplar} design (e g . below 50μm for <^•>(> GH/ designs)

tc> Moreover, FIG. 9 schematically illustrates a non-conductor-backed ACPS feed structure based on the exemplary design shown in FiG. 5B. In this embodiment {he substrate carrier (51 ) would not be electrically connected to the metallic w aveguide housing using a conductiv e bonding materia!, but rather attached to the melailic waveguide housing 5 using some non-conductive epoxy having well known dielectric properties for the frequency range of interest. In FIG, 9, edge wrapping haif-via metallization (56) would be attached to a metallic "ground" pattern (57) on the bottom side of the substrate carrier (51 } in the transition region (54) to prevent propagation of parasitic modes as mentioned above. In effect, the bottom metallization patterns (57) would be suspended over (insulated from) the

10 metal surface of the waveguide housing in the apertures by virtue of the non-conductive epoxy bonding the metal pattern (57) to the melailic waveguide surface. The number, position, width and length of the metal fingers (57) and via wrapping (56) would be designed as needed. The designs can have more wrapping points aiong the length- depending on the required probe length. Again,, the consideration would be given to the

! 5 spacing (filled with a non-conductive epoxy) between the bottoms of the substrate and the opening, which is kept low for an exemplary design (e.g., below 50μm for 60 GH/ designs).

In the exemplary transition apparatus (40) and (50) discussed above, various parameters may be adjusted for purpose of matching the waveguide mode Io the characteristic impedance of the CPW or ACPS transmission lines. For example, the CPW or

20 ACPS Sines can be matched to the waveguide port by adjusting various parameters including, for example, the distance bt between the probe (43)/(53) and the backshort BL the location of the probe (43), (53) in the waveguide cross-section a. the probe width Wp and LP. The goal of the optimization is to achieve the highest possible bandwidth (or maximum bandwidth). On the Smith chart, bandwidth is indicated by a frequency

25 dependent "tear drop^" shaped input reflection coefficient that loops around its center. The smaller the loop, the better the bandwidth. The reactance of the probe is influenced by the energy stored in the supporting substrate. The substrate height, hs. width Ws and length Ls or dielectric constant has a considerable effect on the reactive part of the mpυt impedance and the achieved bandwidth. In the exemplars¹ embodiments discussed above, the

->o supporting substrate does not completely fill the entire waveguide aperture to minimize loading of the probe. However, the substrate can extend all the way across (or beyond taking advantage of the backshort B2 structure, if present) the waveguide channel.

17 In view of the tolerance analysis, the performance of the exemplars' transitions is sensitive to the probe depth Lp within the waveguide. This may not be an issue when the depth can be controlled within few μm taking advantage of the split-block technique that allows the transition substrate with printed probe to be positioned accurately using visual 5 inspection. In this process, alignment can be readily performed based on the finite size top ground conductors patterned on the substrate carrier, the boundary of which is aligned with the internal edge of the waveguide broadside wall (31a). When the transition housing is not fabricated using split-block techniques, the above-mentioned step-in- width alignment mechanism can be appropriately used for positioning purposes, where positioning precision

10 is limited to about 25-30 μm and is based on the EDM machining accuracy of the length L_t of the narrow opening (33b) of the aperture (33).

The aperture (33) that is formed in the broad wall of the waveguide and the proximity of the feed structure operate to perturb the electric field distribution in the vicinity of the probe and, thus, affecting the input impedance of the probe. In this regard.

15 the parameters such as a w indow width W^ and height h. the strip width w and slot width .v for both the CPW and ACPS feeds, and the location of the probe within the opening for the ACPS feed, are additional parameters that influence the input impedance at the CPW and ACPS port.

The size of the opening in the waveguide broadside wall with the inserted feed

20 structure is also of considerable importance, especially for the electrically wide substrate carriers. Due to the classical substrate handling and dicmg limitations, most of the substrates fall into that group at 60GHz and beyond. Thus, the substrate and port opening dimensions are selected so as to not launch the waveguide modes and the associated resonance effects within a di electrical!) loaded opening.

25 Another factor to be considered is an overall width (including top ground conductor widths) of the feed line in the locations where the top and bottom ground conductors are not wrapped When feed structures are too wide, stationary resonance-like effects in the transmission at some frequencies will occur due to an asymmetric field excitation at the discontinuities.

30 Other exemplary features of transition structures according to the invention is that such features can be used within metal enclosures without affecting its performance because

IS if is inherently shielded by the w aveguide wails. Moreover, the apertures (substrate port Py) formed in the broadside wall cai optionally be sealed.

To illustrate the properties of the considered transitions, computer simulations were performed for various CPW-lo-waveguide-transition structures and an ACPS-to-waveguide 5 transition structures designed for wideband operation (50-70OHz) for WR 15 rectangular waveguides. The simulations were performed using a commercially available 3D EM simulation software tool for RF. wireless, packaging; and optoelectronic design, in particular, the HFSS (3D full-wave FEM solver) tool AIi loss mechanisms (ohmic. dielectric and radiation) aid coupling effects in-between the modes were taken into account.

IO A 3D 4μm thick gold metallization with a perfect surface finish (no roughness) was used as conducting layer. Surface impedance formulation is used to account for ohmic losses which is well justified at the frequency range of interest (50-70 OHz). The feed lines wish probes are placed on a 3UUum thick (Used silica substrate (dielectric permittivity of 3.8) which is relatively thick for 50-70GMz frequency band. In exemplar.- embodiments of the invention,.

15 the portion of the substrate beneath the planar probe may be thinned or removed to improve performance of exemplary transition structures described herein. A thick substrate can be chosen for better mechanical stability of the designs. The dimensional parameters for exemplary transition designs are listed in Table 1 below. The results of the simulation indicated that the exemplary transition designs would yield very low insertion loss and

20 return loss within the entire frequency range of interest. Table L

EXEMPLARY DI MENSIONAL PARAMETERS FOR TRANSITION DESIGNS AT WRIS BAND

!^<)

Although exemplary embodiments have been described herein with reference to the accompanying drawings for purposes of il lustra tion, it is to be understood that the present invention ts not limited to those precise embodiments, and that various other changes and modifications may be affected herein by one skilled in the art without departing from the scope of {he invention.

Claims

We Claim;

I . A transition apparatus, comprising. a transition housing comprising a rectangular waveguide channel and an aperture formed through a broad wail of the rectangular wav eguide channel;

5 a substrate having a first surface and a second surface opposite the first surface, and a planar transmission hue and a planar probe formed on the first surface, wherein the planar transmission line comprises a first conductive strip and a second conductive strip, wherein the planar probe is connected to. and extends from, an end of the first conductive strip, and wherein an end of the second conductive strip is terminated by a stub: s 0 wherein the substrate is positioned in the aperture such thai the printed probe protrudes into the rectangular waveguide channel at an offset from a center of the broad wall and wherein the ends of the first and second conductive strip are aligned to an inner s ui" face of the broad wall of the rectangular waveguide channel.

! 5 2. The transition apparatus of claim 1 , wherein one end of the rectangular waveguide channel is close-ended aid provides a backshort for the probe.

3. The transition apparatus of claim I , wherein the backshoil is adjustable.

20 4. The transition apparatus of claim 1 , wherein one end of the rectangular waveguide channel is opened on a mating surface of the transition housing, wherein the mating surface can interface with a rectangular waveguide flange.

5. The transition apparatus of claim 1. wherein the printed transmission line is a 25 CPS {cop! anar slripl me).

6. The transition apparatus of claim L wherein the printed transmission line is an ACPS (asymmetric coplanar stripline).

30 7. The transition apparatus of claim 1, wherein the printed transmission line is a

CPW (coplanar waveguide). 8. The transition apparatus of claim 1 , wherein the aperture has a stepped-width opening to enable alignment and positioning of the substrate in the aperture and the rectangular waveguide channel.

5 9. The transition apparatus of claim 1 , wherein the stub is connected to edge wrap metallization for parasitic mode suppression.

10. The transition apparatus of claim 9, wherein the edge wrap metallization is electrically connected to a metallic surface of the transition housing.

10

1 1 The transition apparatus of claim 9, wherein the edge wrap metallization is connected to a ground plane on a second surface of the substrate.

12. The transition apparatus of claim 9. wherein the edge wrap metallization is

Li "alvanicaliv isolated from the transition housing.

13. The transition apparatus of claim 1 , wherein the transition apparatus is integralh packaged with a MMK" (monolithic microwave integrated Circuit) device.

20 14. The transition apparatus of claim L further comprising a tuning cavity formed on a second broad wall of the rectangular waveguide channel opposite and aligned to the aperture.

15. The transition apparatus of claim i. wherein the transition housing is formed 25 from a block of metallic material.

16. The transition apparatus of claim 1 , wherein the transition housing is formed from a plastic material having surfaces that are coated with a metallic material

3i) 17. A transition apparatus, comprising: a transition housing comprising a rectangular waveguide channel and an aperture formed through a broad wall of the rectangular waveguide channel:

^■> > a substrate haurtg a First surface and a second surface opposite the first sutface and a plaiar transmission line aid a planar probe formed on the first surface, wherein the planar transmission line comprises a first conductiv e stnp and a second eonductn e stop, wherein the plan at probe is connected to. and extends from, an end of the first conductn e strip, and > wherein an end of the second conductn e stnp JS terminated b\ a stub, and wherein {he stub is connected to a conductn e giound pattern on Ui e second sutface of the substrate bv edge- wrap metallization, wherein the substrate is positioned m the aperture such that the printed probe protrudes into the rectangular wav eguide channel aid wherein the ends of the first and 1» second conduct! \ e stπp are aligned to an inner surface of the broad wall of the iectangular wax egmde channel

18 The transition apparatus of claim 17. wheiem one end of the rsctangulai waΛ eguide channel is close-ended and pro\ ides a bacLshort for the probe

19 The transition apparatus of claim 1 H. w herein the backshort is adjustable

20 The ttansiuon appaiatus of claim 18. Λ\ herein one end of the tectanguSar \va\ eguide channel is opened on a mating surface of the transition housing, wherein the

2» mating Mjjface can interface with a jeclangular Λ\ a\ eguκie flatige

21 Hie tiaiipition appaiattis of claim 1 7. wherein the printed transmission line is a t PS (copianar stπplme)

:5 22 The nansiuon appaiatus of claim 17. Λ\ herein the printed transmission line is an ACPS (as\ rometnc copSanar sttiphne)

23 Hie transition apparatus of claim 17. wherein the printed transmission line is a CPW (coplanat wax eginde) it) 24. The transition apparatus of claim 17, wherein the aperture has a stepped- width opening to enable alignment and positioning of the substrate in the aperture and the rectangular waveguide channel.

5 25. The transition apparatus of claim 17, wherein {he conductiv e ground pattern on the second surface of the substrate is conduct! veiy bonded to a metal surface of the transition housing.

26. The transition apparatus of claim ϊ 7. wherein the conductive ground pattern io on the second surface of the substrate is noπ-conducti veiy bonded to a metal surface of the transition housing.

27. The transition apparatus of claim 17, wherein the edge wrap metallization is galvanicaliy isolated from the metallic transition housing,

! 5

28. The transition apparatus of claim 17. wherein the transition apparatus is integrally packaged with a MMϊC.

29. The transition apparatus of claim 17, further comprising a tuning cavity

20 formed on a second broad wall of the rectangular waveguide channel opposite and aligned to the aperture.

30. The transition apparatus of claim 17. wherein the transition housing is formed from a block of metallic material.

25

31. The transition apparatus of claim 17, wherein fhε transition housing is formed from a plastic material having surfaces that are coated with a metallic material.